This invention relates to photonic devices in general, and more particularly to tunable filters and tunable lasers and filter based optical spectrum analyzers.
Tunable Fabry-Perot filters and tunable vertical cavity surface emitting lasers (VCSEL""s) have recently generated considerable interest in the art. This is because these devices are believed to have application for a wide range of different optical components and systems, e.g., wavelength division multiplexing (WDM) fiberoptic systems, switches, routers, highly compact spectroscopic interferometers, optical transceivers, etc.
In some tunable Fabry-Perot filters and in some tunable VCSEL""s, tuning is achieved by using an electrostatic field to move a top mirror relative to a bottom mirror, whereby to change the length of the Fabry-Perot cavity and hence tune the wavelength of the device.
While such a construction is advantageous in that it provides a fast and easy way to tune the device, in practice it has proven difficult to produce relatively uniform devices. Significant performance variations typically occur from device-to-device and from batch-to-batch.
As a result, one object of the present invention is to provide a novel wavelength reference apparatus for use in calibrating a tunable Fabry-Perot filter and/or a tunable VSCEL, whereby the device may be tuned to a precise, known wavelength.
Another object of the present invention is to provide a novel method for calibrating a tunable Fabry-Perot filter and/or a tunable VSCEL, whereby the device may be tuned to a precise, known wavelength.
Still another object of the present invention is to provide a novel fully integrated optical system incorporating the aforementioned wavelength reference apparatus.
These and other objects are addressed by the present invention.
In one form of the invention, there is provided a wavelength reference apparatus for use in calibrating a tunable Fabry-Perot filter or a tunable VCSEL, whereby the device may be tuned to a precise, known wavelength, the wavelength reference apparatus comprising an LED, where the LED is chosen so as to have an emission profile which varies with wavelength; an etalon, where the etalon is chosen so as to have a transmission profile which comprises a comb of transmission peaks, with each transmission peak occurring at a precise, known wavelength; and a detector for detecting the light emitted by the LED and passing through the etalon; whereby when a tunable Fabry-Perot filter or tunable VCSEL is positioned between the etalon and the detector, and the device is swept through its tuning range by varying the tuning voltage applied to the device, the known transmission wavelengths established by the LED and the etalon can be correlated to counterpart tuning voltages of the device, whereby to calibrate the device.
In another form of the invention, there is provided a novel method for calibrating a tunable Fabry-Perot filter or a tunable VCSEL, whereby the device may be tuned to a precise, known wavelength, comprising the steps of: (1) energizing an LED so as to produce an emission of light, the LED being chosen so as to have an emission profile which varies with wavelength; (2) passing the light output by the LED through an etalon so as to generate a comb of known transmission peaks, with each transmission peak occurring at a precise, known wavelength; (3) passing light from the etalon to the device; and (4) sweeping the device through its tuning range by varying the tuning voltage applied to the device, whereby a correlation may be established between the known wavelength of each transmission peak and the tuning voltage associated with that wavelength, whereby to calibrate the device.
And in another form of the invention, there is provided a novel fully integrated optical system for monitoring the channels of an optical fiber in a WDM fiberoptic system, the fully integrated optical system comprising an input from the optical fiber; a tunable filter having a first end and a second end, the tunable filter being positioned so as to receive light from the input at its first end; a first beam splitter for receiving light emerging from the second end of the tunable filter; a first detector for receiving light from the first beam splitter and detecting the same; and wavelength reference apparatus for use in calibrating the tunable filter, whereby the tunable filter may be tuned to a precise, known wavelength, the wavelength reference apparatus comprising: an LED positioned so that light emitted by the LED enters the second end of the tunable filter, the LED having an emission profile which varies with wavelength; a second beam splitter for receiving light emerging from the first end of the tunable filter; an etalon for receiving light from the second beam splitter, the etalon having a transmission profile which comprises a comb of transmission peaks, with each transmission peak occurring at a precise, known wavelength; and a second detector for detecting the light passing through the etalon; whereby when the LED is energized and the tunable filter is swept through its tuning range by varying the tuning voltage applied to the tunable filter, the known transmission wavelengths established by the LED and the etalon can be correlated to counterpart tuning voltages of the tunable filter, whereby to calibrate the tunable filter; and whereby when light from the input is passed through the tunable filter, the tunable filter may be tuned to a selected channel and the first detector may be used to detect light present on that channel.
And in another form of the invention, there is provided a novel fully integrated optical system for monitoring the channels of an optical fiber in a WDM fiberoptic system, the fully integrated optical system comprising an input from the optical fiber; a tunable filter having a first end and a second end, the tunable filter being positioned so as to receive light from the input at its first end; a detector for receiving light from the tunable filter and detecting the same; and wavelength reference apparatus for use in calibrating the tunable filter, whereby the tunable filter may be tuned to a precise, known wavelength, the wavelength reference apparatus comprising: an LED, the LED having an emission profile which varies with wavelength; an etalon for receiving light from the LED, the etalon having a transmission profile which comprises a comb of transmission peaks, with each transmission peak occurring at a precise, known wavelength; and a shutter having (i) a first position wherein light from the etalon will be directed through the tunable filter and onto the detector, and (ii) a second position wherein light from the input will be directed through the tunable filter and onto the detector; whereby when the shutter is placed in its first position and the LED is energized and the tunable filter is swept through its tuning range by varying the tuning voltage applied to the tunable filter, the known transmission wavelengths established by the LED and the etalon can be correlated to counterpart tuning voltages of the tunable filter, whereby to calibrate the tunable filter; and whereby when the shutter is placed in its second position and light from the input is passed through the tunable filter, the tunable filter may be tuned to a selected channel and the detector may be used to detect light present on that channel.